1. Field of the Invention
The invention relates to a fine-particled polyarylene ether ketone (PAEK), its preparation by milling of porous PAEK and its use.
2. Discussion of the Background
The milling of polymers using a very wide range of milling units and milling processes is an established technology which is already in use for a very wide range of milled products, for example for polyesters, polyamides or polyolefins. These polymers are usually milled from the corresponding commercial granular form in a cryogenic milling process to give the corresponding powder. For this purpose, pinned-disk mills or fluidized-bed mills are usually used at operating temperatures of up to −60° C. PAEK and in particular polyether ether ketone (PEEK) are distinguished, inter alia, by outstanding tribological and mechanical properties; they can therefore be milled only with very great difficulty and at high costs to give a fine powder. DE 38 44 457 A1 describes the cold milling of PAEK on a fluidized-bed mill, fine powders having a mean particle size of 40 μm or less being obtained. A disadvantage here, however, is the yield, which, at not more than 7.5 kg/h, remains substantially below the usual throughputs of a milling apparatus. The technical difficulties of milling a PAEK are evident here.
There has therefore been occasional approaches to bypass the milling step in powder production and to obtain pulverulent or very finely pulverulent PAEK by alternative routes, Thus, U.S. Pat. No. 5,910,558 describes the preparation of PAEK micropowders by prilling of melts or by spray-drying of the solutions. However, this process has not become established, owing to the high cost of apparatus and the low process stability.
A further method disclosed in WO 99/50339 comprises mixing PAEK with another polymer and thus establishing the particle shape of the PAEK. After dissolution of the other polymer in a suitable solvent, the pulverulent PAEK is exposed. However, this method is very complicated.